/*
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 */

package java.io;

import java.net.URI;
import java.net.URL;
import java.net.MalformedURLException;
import java.net.URISyntaxException;
import java.util.List;
import java.util.ArrayList;
import java.security.AccessController;
import java.security.SecureRandom;
import java.nio.file.Path;
import java.nio.file.FileSystems;
import sun.security.action.GetPropertyAction;

/**
 * An abstract representation of file and directory pathnames.
 *
 * <p> User interfaces and operating systems use system-dependent <em>pathname
 * strings</em> to name files and directories.  This class presents an
 * abstract, system-independent view of hierarchical pathnames.  An
 * <em>abstract pathname</em> has two components:
 *
 * <ol>
 * <li> An optional system-dependent <em>prefix</em> string,
 * such as a disk-drive specifier, <code>"/"</code>&nbsp;for the UNIX root
 * directory, or <code>"\\\\"</code>&nbsp;for a Microsoft Windows UNC pathname, and
 * <li> A sequence of zero or more string <em>names</em>.
 * </ol>
 *
 * The first name in an abstract pathname may be a directory name or, in the
 * case of Microsoft Windows UNC pathnames, a hostname.  Each subsequent name
 * in an abstract pathname denotes a directory; the last name may denote
 * either a directory or a file.  The <em>empty</em> abstract pathname has no
 * prefix and an empty name sequence.
 *
 * <p> The conversion of a pathname string to or from an abstract pathname is
 * inherently system-dependent.  When an abstract pathname is converted into a
 * pathname string, each name is separated from the next by a single copy of
 * the default <em>separator character</em>.  The default name-separator
 * character is defined by the system property <code>file.separator</code>, and
 * is made available in the public static fields <code>{@link
 * #separator}</code> and <code>{@link #separatorChar}</code> of this class.
 * When a pathname string is converted into an abstract pathname, the names
 * within it may be separated by the default name-separator character or by any
 * other name-separator character that is supported by the underlying system.
 *
 * <p> A pathname, whether abstract or in string form, may be either
 * <em>absolute</em> or <em>relative</em>.  An absolute pathname is complete in
 * that no other information is required in order to locate the file that it
 * denotes.  A relative pathname, in contrast, must be interpreted in terms of
 * information taken from some other pathname.  By default the classes in the
 * <code>java.io</code> package always resolve relative pathnames against the
 * current user directory.  This directory is named by the system property
 * <code>user.dir</code>, and is typically the directory in which the Java
 * virtual machine was invoked.
 *
 * <p> The <em>parent</em> of an abstract pathname may be obtained by invoking
 * the {@link #getParent} method of this class and consists of the pathname's
 * prefix and each name in the pathname's name sequence except for the last.
 * Each directory's absolute pathname is an ancestor of any <tt>File</tt>
 * object with an absolute abstract pathname which begins with the directory's
 * absolute pathname.  For example, the directory denoted by the abstract
 * pathname <tt>"/usr"</tt> is an ancestor of the directory denoted by the
 * pathname <tt>"/usr/local/bin"</tt>.
 *
 * <p> The prefix concept is used to handle root directories on UNIX platforms,
 * and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms,
 * as follows:
 *
 * <ul>
 *
 * <li> For UNIX platforms, the prefix of an absolute pathname is always
 * <code>"/"</code>.  Relative pathnames have no prefix.  The abstract pathname
 * denoting the root directory has the prefix <code>"/"</code> and an empty
 * name sequence.
 *
 * <li> For Microsoft Windows platforms, the prefix of a pathname that contains a drive
 * specifier consists of the drive letter followed by <code>":"</code> and
 * possibly followed by <code>"\\"</code> if the pathname is absolute.  The
 * prefix of a UNC pathname is <code>"\\\\"</code>; the hostname and the share
 * name are the first two names in the name sequence.  A relative pathname that
 * does not specify a drive has no prefix.
 *
 * </ul>
 *
 * <p> Instances of this class may or may not denote an actual file-system
 * object such as a file or a directory.  If it does denote such an object
 * then that object resides in a <i>partition</i>.  A partition is an
 * operating system-specific portion of storage for a file system.  A single
 * storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may
 * contain multiple partitions.  The object, if any, will reside on the
 * partition <a name="partName">named</a> by some ancestor of the absolute
 * form of this pathname.
 *
 * <p> A file system may implement restrictions to certain operations on the
 * actual file-system object, such as reading, writing, and executing.  These
 * restrictions are collectively known as <i>access permissions</i>.  The file
 * system may have multiple sets of access permissions on a single object.
 * For example, one set may apply to the object's <i>owner</i>, and another
 * may apply to all other users.  The access permissions on an object may
 * cause some methods in this class to fail.
 *
 * <p> Instances of the <code>File</code> class are immutable; that is, once
 * created, the abstract pathname represented by a <code>File</code> object
 * will never change.
 *
 * <h3>Interoperability with {@code java.nio.file} package</h3>
 *
 * <p> The <a href="../../java/nio/file/package-summary.html">{@code java.nio.file}</a>
 * package defines interfaces and classes for the Java virtual machine to access
 * files, file attributes, and file systems. This API may be used to overcome
 * many of the limitations of the {@code java.io.File} class.
 * The {@link #toPath toPath} method may be used to obtain a {@link
 * Path} that uses the abstract path represented by a {@code File} object to
 * locate a file. The resulting {@code Path} may be used with the {@link
 * java.nio.file.Files} class to provide more efficient and extensive access to
 * additional file operations, file attributes, and I/O exceptions to help
 * diagnose errors when an operation on a file fails.
 *
 * @author unascribed
 * @since JDK1.0
 */

public class File
    implements Serializable, Comparable<File> {

  /**
   * The FileSystem object representing the platform's local file system.
   */
  private static final FileSystem fs = DefaultFileSystem.getFileSystem();

  /**
   * This abstract pathname's normalized pathname string. A normalized
   * pathname string uses the default name-separator character and does not
   * contain any duplicate or redundant separators.
   *
   * @serial
   */
  private final String path;

  /**
   * Enum type that indicates the status of a file path.
   */
  private static enum PathStatus {
    INVALID, CHECKED
  }

  ;

  /**
   * The flag indicating whether the file path is invalid.
   */
  private transient PathStatus status = null;

  /**
   * Check if the file has an invalid path. Currently, the inspection of
   * a file path is very limited, and it only covers Nul character check.
   * Returning true means the path is definitely invalid/garbage. But
   * returning false does not guarantee that the path is valid.
   *
   * @return true if the file path is invalid.
   */
  final boolean isInvalid() {
    if (status == null) {
      status = (this.path.indexOf('\u0000') < 0) ? PathStatus.CHECKED
          : PathStatus.INVALID;
    }
    return status == PathStatus.INVALID;
  }

  /**
   * The length of this abstract pathname's prefix, or zero if it has no
   * prefix.
   */
  private final transient int prefixLength;

  /**
   * Returns the length of this abstract pathname's prefix.
   * For use by FileSystem classes.
   */
  int getPrefixLength() {
    return prefixLength;
  }

  /**
   * The system-dependent default name-separator character.  This field is
   * initialized to contain the first character of the value of the system
   * property <code>file.separator</code>.  On UNIX systems the value of this
   * field is <code>'/'</code>; on Microsoft Windows systems it is <code>'\\'</code>.
   *
   * @see java.lang.System#getProperty(java.lang.String)
   */
  public static final char separatorChar = fs.getSeparator();

  /**
   * The system-dependent default name-separator character, represented as a
   * string for convenience.  This string contains a single character, namely
   * <code>{@link #separatorChar}</code>.
   */
  public static final String separator = "" + separatorChar;

  /**
   * The system-dependent path-separator character.  This field is
   * initialized to contain the first character of the value of the system
   * property <code>path.separator</code>.  This character is used to
   * separate filenames in a sequence of files given as a <em>path list</em>.
   * On UNIX systems, this character is <code>':'</code>; on Microsoft Windows systems it
   * is <code>';'</code>.
   *
   * @see java.lang.System#getProperty(java.lang.String)
   */
  public static final char pathSeparatorChar = fs.getPathSeparator();

  /**
   * The system-dependent path-separator character, represented as a string
   * for convenience.  This string contains a single character, namely
   * <code>{@link #pathSeparatorChar}</code>.
   */
  public static final String pathSeparator = "" + pathSeparatorChar;


    /* -- Constructors -- */

  /**
   * Internal constructor for already-normalized pathname strings.
   */
  private File(String pathname, int prefixLength) {
    this.path = pathname;
    this.prefixLength = prefixLength;
  }

  /**
   * Internal constructor for already-normalized pathname strings.
   * The parameter order is used to disambiguate this method from the
   * public(File, String) constructor.
   */
  private File(String child, File parent) {
    assert parent.path != null;
    assert (!parent.path.equals(""));
    this.path = fs.resolve(parent.path, child);
    this.prefixLength = parent.prefixLength;
  }

  /**
   * Creates a new <code>File</code> instance by converting the given
   * pathname string into an abstract pathname.  If the given string is
   * the empty string, then the result is the empty abstract pathname.
   *
   * @param pathname A pathname string
   * @throws NullPointerException If the <code>pathname</code> argument is <code>null</code>
   */
  public File(String pathname) {
    if (pathname == null) {
      throw new NullPointerException();
    }
    this.path = fs.normalize(pathname);
    this.prefixLength = fs.prefixLength(this.path);
  }

    /* Note: The two-argument File constructors do not interpret an empty
       parent abstract pathname as the current user directory.  An empty parent
       instead causes the child to be resolved against the system-dependent
       directory defined by the FileSystem.getDefaultParent method.  On Unix
       this default is "/", while on Microsoft Windows it is "\\".  This is required for
       compatibility with the original behavior of this class. */

  /**
   * Creates a new <code>File</code> instance from a parent pathname string
   * and a child pathname string.
   *
   * <p> If <code>parent</code> is <code>null</code> then the new
   * <code>File</code> instance is created as if by invoking the
   * single-argument <code>File</code> constructor on the given
   * <code>child</code> pathname string.
   *
   * <p> Otherwise the <code>parent</code> pathname string is taken to denote
   * a directory, and the <code>child</code> pathname string is taken to
   * denote either a directory or a file.  If the <code>child</code> pathname
   * string is absolute then it is converted into a relative pathname in a
   * system-dependent way.  If <code>parent</code> is the empty string then
   * the new <code>File</code> instance is created by converting
   * <code>child</code> into an abstract pathname and resolving the result
   * against a system-dependent default directory.  Otherwise each pathname
   * string is converted into an abstract pathname and the child abstract
   * pathname is resolved against the parent.
   *
   * @param parent The parent pathname string
   * @param child The child pathname string
   * @throws NullPointerException If <code>child</code> is <code>null</code>
   */
  public File(String parent, String child) {
    if (child == null) {
      throw new NullPointerException();
    }
    if (parent != null) {
      if (parent.equals("")) {
        this.path = fs.resolve(fs.getDefaultParent(),
            fs.normalize(child));
      } else {
        this.path = fs.resolve(fs.normalize(parent),
            fs.normalize(child));
      }
    } else {
      this.path = fs.normalize(child);
    }
    this.prefixLength = fs.prefixLength(this.path);
  }

  /**
   * Creates a new <code>File</code> instance from a parent abstract
   * pathname and a child pathname string.
   *
   * <p> If <code>parent</code> is <code>null</code> then the new
   * <code>File</code> instance is created as if by invoking the
   * single-argument <code>File</code> constructor on the given
   * <code>child</code> pathname string.
   *
   * <p> Otherwise the <code>parent</code> abstract pathname is taken to
   * denote a directory, and the <code>child</code> pathname string is taken
   * to denote either a directory or a file.  If the <code>child</code>
   * pathname string is absolute then it is converted into a relative
   * pathname in a system-dependent way.  If <code>parent</code> is the empty
   * abstract pathname then the new <code>File</code> instance is created by
   * converting <code>child</code> into an abstract pathname and resolving
   * the result against a system-dependent default directory.  Otherwise each
   * pathname string is converted into an abstract pathname and the child
   * abstract pathname is resolved against the parent.
   *
   * @param parent The parent abstract pathname
   * @param child The child pathname string
   * @throws NullPointerException If <code>child</code> is <code>null</code>
   */
  public File(File parent, String child) {
    if (child == null) {
      throw new NullPointerException();
    }
    if (parent != null) {
      if (parent.path.equals("")) {
        this.path = fs.resolve(fs.getDefaultParent(),
            fs.normalize(child));
      } else {
        this.path = fs.resolve(parent.path,
            fs.normalize(child));
      }
    } else {
      this.path = fs.normalize(child);
    }
    this.prefixLength = fs.prefixLength(this.path);
  }

  /**
   * Creates a new <tt>File</tt> instance by converting the given <tt>file:</tt> URI into an
   * abstract pathname.
   *
   * <p> The exact form of a <tt>file:</tt> URI is system-dependent, hence the transformation
   * performed by this constructor is also system-dependent.
   *
   * <p> For a given abstract pathname <i>f</i> it is guaranteed that
   *
   * <blockquote><tt> new File(</tt><i>&nbsp;f</i><tt>.{@link #toURI()
   * toURI}()).equals(</tt><i>&nbsp;f</i><tt>.{@link #getAbsoluteFile() getAbsoluteFile}())
   * </tt></blockquote>
   *
   * so long as the original abstract pathname, the URI, and the new abstract pathname are all
   * created in (possibly different invocations of) the same Java virtual machine.  This
   * relationship typically does not hold, however, when a <tt>file:</tt> URI that is created in a
   * virtual machine on one operating system is converted into an abstract pathname in a virtual
   * machine on a different operating system.
   *
   * @param uri An absolute, hierarchical URI with a scheme equal to <tt>"file"</tt>, a non-empty
   * path component, and undefined authority, query, and fragment components
   * @throws NullPointerException If <tt>uri</tt> is <tt>null</tt>
   * @throws IllegalArgumentException If the preconditions on the parameter do not hold
   * @see #toURI()
   * @see java.net.URI
   * @since 1.4
   */
  public File(URI uri) {

    // Check our many preconditions
    if (!uri.isAbsolute()) {
      throw new IllegalArgumentException("URI is not absolute");
    }
    if (uri.isOpaque()) {
      throw new IllegalArgumentException("URI is not hierarchical");
    }
    String scheme = uri.getScheme();
    if ((scheme == null) || !scheme.equalsIgnoreCase("file")) {
      throw new IllegalArgumentException("URI scheme is not \"file\"");
    }
    if (uri.getAuthority() != null) {
      throw new IllegalArgumentException("URI has an authority component");
    }
    if (uri.getFragment() != null) {
      throw new IllegalArgumentException("URI has a fragment component");
    }
    if (uri.getQuery() != null) {
      throw new IllegalArgumentException("URI has a query component");
    }
    String p = uri.getPath();
    if (p.equals("")) {
      throw new IllegalArgumentException("URI path component is empty");
    }

    // Okay, now initialize
    p = fs.fromURIPath(p);
    if (File.separatorChar != '/') {
      p = p.replace('/', File.separatorChar);
    }
    this.path = fs.normalize(p);
    this.prefixLength = fs.prefixLength(this.path);
  }


    /* -- Path-component accessors -- */

  /**
   * Returns the name of the file or directory denoted by this abstract
   * pathname.  This is just the last name in the pathname's name
   * sequence.  If the pathname's name sequence is empty, then the empty
   * string is returned.
   *
   * @return The name of the file or directory denoted by this abstract pathname, or the empty
   * string if this pathname's name sequence is empty
   */
  public String getName() {
    int index = path.lastIndexOf(separatorChar);
    if (index < prefixLength) {
      return path.substring(prefixLength);
    }
    return path.substring(index + 1);
  }

  /**
   * Returns the pathname string of this abstract pathname's parent, or
   * <code>null</code> if this pathname does not name a parent directory.
   *
   * <p> The <em>parent</em> of an abstract pathname consists of the
   * pathname's prefix, if any, and each name in the pathname's name
   * sequence except for the last.  If the name sequence is empty then
   * the pathname does not name a parent directory.
   *
   * @return The pathname string of the parent directory named by this abstract pathname, or
   * <code>null</code> if this pathname does not name a parent
   */
  public String getParent() {
    int index = path.lastIndexOf(separatorChar);
    if (index < prefixLength) {
      if ((prefixLength > 0) && (path.length() > prefixLength)) {
        return path.substring(0, prefixLength);
      }
      return null;
    }
    return path.substring(0, index);
  }

  /**
   * Returns the abstract pathname of this abstract pathname's parent,
   * or <code>null</code> if this pathname does not name a parent
   * directory.
   *
   * <p> The <em>parent</em> of an abstract pathname consists of the
   * pathname's prefix, if any, and each name in the pathname's name
   * sequence except for the last.  If the name sequence is empty then
   * the pathname does not name a parent directory.
   *
   * @return The abstract pathname of the parent directory named by this abstract pathname, or
   * <code>null</code> if this pathname does not name a parent
   * @since 1.2
   */
  public File getParentFile() {
    String p = this.getParent();
    if (p == null) {
      return null;
    }
    return new File(p, this.prefixLength);
  }

  /**
   * Converts this abstract pathname into a pathname string.  The resulting
   * string uses the {@link #separator default name-separator character} to
   * separate the names in the name sequence.
   *
   * @return The string form of this abstract pathname
   */
  public String getPath() {
    return path;
  }


    /* -- Path operations -- */

  /**
   * Tests whether this abstract pathname is absolute.  The definition of
   * absolute pathname is system dependent.  On UNIX systems, a pathname is
   * absolute if its prefix is <code>"/"</code>.  On Microsoft Windows systems, a
   * pathname is absolute if its prefix is a drive specifier followed by
   * <code>"\\"</code>, or if its prefix is <code>"\\\\"</code>.
   *
   * @return <code>true</code> if this abstract pathname is absolute, <code>false</code> otherwise
   */
  public boolean isAbsolute() {
    return fs.isAbsolute(this);
  }

  /**
   * Returns the absolute pathname string of this abstract pathname.
   *
   * <p> If this abstract pathname is already absolute, then the pathname
   * string is simply returned as if by the <code>{@link #getPath}</code>
   * method.  If this abstract pathname is the empty abstract pathname then
   * the pathname string of the current user directory, which is named by the
   * system property <code>user.dir</code>, is returned.  Otherwise this
   * pathname is resolved in a system-dependent way.  On UNIX systems, a
   * relative pathname is made absolute by resolving it against the current
   * user directory.  On Microsoft Windows systems, a relative pathname is made absolute
   * by resolving it against the current directory of the drive named by the
   * pathname, if any; if not, it is resolved against the current user
   * directory.
   *
   * @return The absolute pathname string denoting the same file or directory as this abstract
   * pathname
   * @throws SecurityException If a required system property value cannot be accessed.
   * @see java.io.File#isAbsolute()
   */
  public String getAbsolutePath() {
    return fs.resolve(this);
  }

  /**
   * Returns the absolute form of this abstract pathname.  Equivalent to
   * <code>new&nbsp;File(this.{@link #getAbsolutePath})</code>.
   *
   * @return The absolute abstract pathname denoting the same file or directory as this abstract
   * pathname
   * @throws SecurityException If a required system property value cannot be accessed.
   * @since 1.2
   */
  public File getAbsoluteFile() {
    String absPath = getAbsolutePath();
    return new File(absPath, fs.prefixLength(absPath));
  }

  /**
   * Returns the canonical pathname string of this abstract pathname.
   *
   * <p> A canonical pathname is both absolute and unique.  The precise
   * definition of canonical form is system-dependent.  This method first
   * converts this pathname to absolute form if necessary, as if by invoking the
   * {@link #getAbsolutePath} method, and then maps it to its unique form in a
   * system-dependent way.  This typically involves removing redundant names
   * such as <tt>"."</tt> and <tt>".."</tt> from the pathname, resolving
   * symbolic links (on UNIX platforms), and converting drive letters to a
   * standard case (on Microsoft Windows platforms).
   *
   * <p> Every pathname that denotes an existing file or directory has a
   * unique canonical form.  Every pathname that denotes a nonexistent file
   * or directory also has a unique canonical form.  The canonical form of
   * the pathname of a nonexistent file or directory may be different from
   * the canonical form of the same pathname after the file or directory is
   * created.  Similarly, the canonical form of the pathname of an existing
   * file or directory may be different from the canonical form of the same
   * pathname after the file or directory is deleted.
   *
   * @return The canonical pathname string denoting the same file or directory as this abstract
   * pathname
   * @throws IOException If an I/O error occurs, which is possible because the construction of the
   * canonical pathname may require filesystem queries
   * @throws SecurityException If a required system property value cannot be accessed, or if a
   * security manager exists and its <code>{@link java.lang.SecurityManager#checkRead}</code> method
   * denies read access to the file
   * @see Path#toRealPath
   * @since JDK1.1
   */
  public String getCanonicalPath() throws IOException {
    if (isInvalid()) {
      throw new IOException("Invalid file path");
    }
    return fs.canonicalize(fs.resolve(this));
  }

  /**
   * Returns the canonical form of this abstract pathname.  Equivalent to
   * <code>new&nbsp;File(this.{@link #getCanonicalPath})</code>.
   *
   * @return The canonical pathname string denoting the same file or directory as this abstract
   * pathname
   * @throws IOException If an I/O error occurs, which is possible because the construction of the
   * canonical pathname may require filesystem queries
   * @throws SecurityException If a required system property value cannot be accessed, or if a
   * security manager exists and its <code>{@link java.lang.SecurityManager#checkRead}</code> method
   * denies read access to the file
   * @see Path#toRealPath
   * @since 1.2
   */
  public File getCanonicalFile() throws IOException {
    String canonPath = getCanonicalPath();
    return new File(canonPath, fs.prefixLength(canonPath));
  }

  private static String slashify(String path, boolean isDirectory) {
    String p = path;
    if (File.separatorChar != '/') {
      p = p.replace(File.separatorChar, '/');
    }
    if (!p.startsWith("/")) {
      p = "/" + p;
    }
    if (!p.endsWith("/") && isDirectory) {
      p = p + "/";
    }
    return p;
  }

  /**
   * Converts this abstract pathname into a <code>file:</code> URL.  The
   * exact form of the URL is system-dependent.  If it can be determined that
   * the file denoted by this abstract pathname is a directory, then the
   * resulting URL will end with a slash.
   *
   * @return A URL object representing the equivalent file URL
   * @throws MalformedURLException If the path cannot be parsed as a URL
   * @see #toURI()
   * @see java.net.URI
   * @see java.net.URI#toURL()
   * @see java.net.URL
   * @since 1.2
   * @deprecated This method does not automatically escape characters that are illegal in URLs.  It
   * is recommended that new code convert an abstract pathname into a URL by first converting it
   * into a URI, via the {@link #toURI() toURI} method, and then converting the URI into a URL via
   * the {@link java.net.URI#toURL() URI.toURL} method.
   */
  @Deprecated
  public URL toURL() throws MalformedURLException {
    if (isInvalid()) {
      throw new MalformedURLException("Invalid file path");
    }
    return new URL("file", "", slashify(getAbsolutePath(), isDirectory()));
  }

  /**
   * Constructs a <tt>file:</tt> URI that represents this abstract pathname.
   *
   * <p> The exact form of the URI is system-dependent.  If it can be determined that the file
   * denoted by this abstract pathname is a directory, then the resulting URI will end with a
   * slash.
   *
   * <p> For a given abstract pathname <i>f</i>, it is guaranteed that
   *
   * <blockquote><tt> new {@link #File(java.net.URI) File}(</tt><i>&nbsp;f</i><tt>.toURI()).equals(</tt><i>&nbsp;f</i><tt>.{@link
   * #getAbsoluteFile() getAbsoluteFile}()) </tt></blockquote>
   *
   * so long as the original abstract pathname, the URI, and the new abstract pathname are all
   * created in (possibly different invocations of) the same Java virtual machine.  Due to the
   * system-dependent nature of abstract pathnames, however, this relationship typically does not
   * hold when a <tt>file:</tt> URI that is created in a virtual machine on one operating system is
   * converted into an abstract pathname in a virtual machine on a different operating system.
   *
   * <p> Note that when this abstract pathname represents a UNC pathname then all components of the
   * UNC (including the server name component) are encoded in the {@code URI} path. The authority
   * component is undefined, meaning that it is represented as {@code null}. The {@link Path} class
   * defines the {@link Path#toUri toUri} method to encode the server name in the authority
   * component of the resulting {@code URI}. The {@link #toPath toPath} method may be used to obtain
   * a {@code Path} representing this abstract pathname.
   *
   * @return An absolute, hierarchical URI with a scheme equal to <tt>"file"</tt>, a path
   * representing this abstract pathname, and undefined authority, query, and fragment components
   * @throws SecurityException If a required system property value cannot be accessed.
   * @see #File(java.net.URI)
   * @see java.net.URI
   * @see java.net.URI#toURL()
   * @since 1.4
   */
  public URI toURI() {
    try {
      File f = getAbsoluteFile();
      String sp = slashify(f.getPath(), f.isDirectory());
      if (sp.startsWith("//")) {
        sp = "//" + sp;
      }
      return new URI("file", null, sp, null);
    } catch (URISyntaxException x) {
      throw new Error(x);         // Can't happen
    }
  }


    /* -- Attribute accessors -- */

  /**
   * Tests whether the application can read the file denoted by this
   * abstract pathname. On some platforms it may be possible to start the
   * Java virtual machine with special privileges that allow it to read
   * files that are marked as unreadable. Consequently this method may return
   * {@code true} even though the file does not have read permissions.
   *
   * @return <code>true</code> if and only if the file specified by this abstract pathname exists
   * <em>and</em> can be read by the application; <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method denies read access to the
   * file
   */
  public boolean canRead() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.checkAccess(this, FileSystem.ACCESS_READ);
  }

  /**
   * Tests whether the application can modify the file denoted by this
   * abstract pathname. On some platforms it may be possible to start the
   * Java virtual machine with special privileges that allow it to modify
   * files that are marked read-only. Consequently this method may return
   * {@code true} even though the file is marked read-only.
   *
   * @return <code>true</code> if and only if the file system actually contains a file denoted by
   * this abstract pathname <em>and</em> the application is allowed to write to the file;
   * <code>false</code> otherwise.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the file
   */
  public boolean canWrite() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.checkAccess(this, FileSystem.ACCESS_WRITE);
  }

  /**
   * Tests whether the file or directory denoted by this abstract pathname
   * exists.
   *
   * @return <code>true</code> if and only if the file or directory denoted by this abstract
   * pathname exists; <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method denies read access to the
   * file or directory
   */
  public boolean exists() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return false;
    }
    return ((fs.getBooleanAttributes(this) & FileSystem.BA_EXISTS) != 0);
  }

  /**
   * Tests whether the file denoted by this abstract pathname is a
   * directory.
   *
   * <p> Where it is required to distinguish an I/O exception from the case
   * that the file is not a directory, or where several attributes of the
   * same file are required at the same time, then the {@link
   * java.nio.file.Files#readAttributes(Path, Class, LinkOption[])
   * Files.readAttributes} method may be used.
   *
   * @return <code>true</code> if and only if the file denoted by this abstract pathname exists
   * <em>and</em> is a directory; <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method denies read access to the
   * file
   */
  public boolean isDirectory() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return false;
    }
    return ((fs.getBooleanAttributes(this) & FileSystem.BA_DIRECTORY)
        != 0);
  }

  /**
   * Tests whether the file denoted by this abstract pathname is a normal
   * file.  A file is <em>normal</em> if it is not a directory and, in
   * addition, satisfies other system-dependent criteria.  Any non-directory
   * file created by a Java application is guaranteed to be a normal file.
   *
   * <p> Where it is required to distinguish an I/O exception from the case
   * that the file is not a normal file, or where several attributes of the
   * same file are required at the same time, then the {@link
   * java.nio.file.Files#readAttributes(Path, Class, LinkOption[])
   * Files.readAttributes} method may be used.
   *
   * @return <code>true</code> if and only if the file denoted by this abstract pathname exists
   * <em>and</em> is a normal file; <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method denies read access to the
   * file
   */
  public boolean isFile() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return false;
    }
    return ((fs.getBooleanAttributes(this) & FileSystem.BA_REGULAR) != 0);
  }

  /**
   * Tests whether the file named by this abstract pathname is a hidden
   * file.  The exact definition of <em>hidden</em> is system-dependent.  On
   * UNIX systems, a file is considered to be hidden if its name begins with
   * a period character (<code>'.'</code>).  On Microsoft Windows systems, a file is
   * considered to be hidden if it has been marked as such in the filesystem.
   *
   * @return <code>true</code> if and only if the file denoted by this abstract pathname is hidden
   * according to the conventions of the underlying platform
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method denies read access to the
   * file
   * @since 1.2
   */
  public boolean isHidden() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return false;
    }
    return ((fs.getBooleanAttributes(this) & FileSystem.BA_HIDDEN) != 0);
  }

  /**
   * Returns the time that the file denoted by this abstract pathname was
   * last modified.
   *
   * <p> Where it is required to distinguish an I/O exception from the case
   * where {@code 0L} is returned, or where several attributes of the
   * same file are required at the same time, or where the time of last
   * access or the creation time are required, then the {@link
   * java.nio.file.Files#readAttributes(Path, Class, LinkOption[])
   * Files.readAttributes} method may be used.
   *
   * @return A <code>long</code> value representing the time the file was last modified, measured in
   * milliseconds since the epoch (00:00:00 GMT, January 1, 1970), or <code>0L</code> if the file
   * does not exist or if an I/O error occurs
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method denies read access to the
   * file
   */
  public long lastModified() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return 0L;
    }
    return fs.getLastModifiedTime(this);
  }

  /**
   * Returns the length of the file denoted by this abstract pathname.
   * The return value is unspecified if this pathname denotes a directory.
   *
   * <p> Where it is required to distinguish an I/O exception from the case
   * that {@code 0L} is returned, or where several attributes of the same file
   * are required at the same time, then the {@link
   * java.nio.file.Files#readAttributes(Path, Class, LinkOption[])
   * Files.readAttributes} method may be used.
   *
   * @return The length, in bytes, of the file denoted by this abstract pathname, or <code>0L</code>
   * if the file does not exist.  Some operating systems may return <code>0L</code> for pathnames
   * denoting system-dependent entities such as devices or pipes.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method denies read access to the
   * file
   */
  public long length() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return 0L;
    }
    return fs.getLength(this);
  }


    /* -- File operations -- */

  /**
   * Atomically creates a new, empty file named by this abstract pathname if
   * and only if a file with this name does not yet exist.  The check for the
   * existence of the file and the creation of the file if it does not exist
   * are a single operation that is atomic with respect to all other
   * filesystem activities that might affect the file.
   * <P>
   * Note: this method should <i>not</i> be used for file-locking, as
   * the resulting protocol cannot be made to work reliably. The
   * {@link java.nio.channels.FileLock FileLock}
   * facility should be used instead.
   *
   * @return <code>true</code> if the named file does not exist and was successfully created;
   * <code>false</code> if the named file already exists
   * @throws IOException If an I/O error occurred
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the file
   * @since 1.2
   */
  public boolean createNewFile() throws IOException {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      throw new IOException("Invalid file path");
    }
    return fs.createFileExclusively(path);
  }

  /**
   * Deletes the file or directory denoted by this abstract pathname.  If
   * this pathname denotes a directory, then the directory must be empty in
   * order to be deleted.
   *
   * <p> Note that the {@link java.nio.file.Files} class defines the {@link
   * java.nio.file.Files#delete(Path) delete} method to throw an {@link IOException}
   * when a file cannot be deleted. This is useful for error reporting and to
   * diagnose why a file cannot be deleted.
   *
   * @return <code>true</code> if and only if the file or directory is successfully deleted;
   * <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkDelete}</code> method denies delete access to the file
   */
  public boolean delete() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkDelete(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.delete(this);
  }

  /**
   * Requests that the file or directory denoted by this abstract
   * pathname be deleted when the virtual machine terminates.
   * Files (or directories) are deleted in the reverse order that
   * they are registered. Invoking this method to delete a file or
   * directory that is already registered for deletion has no effect.
   * Deletion will be attempted only for normal termination of the
   * virtual machine, as defined by the Java Language Specification.
   *
   * <p> Once deletion has been requested, it is not possible to cancel the
   * request.  This method should therefore be used with care.
   *
   * <P>
   * Note: this method should <i>not</i> be used for file-locking, as
   * the resulting protocol cannot be made to work reliably. The
   * {@link java.nio.channels.FileLock FileLock}
   * facility should be used instead.
   *
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkDelete}</code> method denies delete access to the file
   * @see #delete
   * @since 1.2
   */
  public void deleteOnExit() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkDelete(path);
    }
    if (isInvalid()) {
      return;
    }
    DeleteOnExitHook.add(path);
  }

  /**
   * Returns an array of strings naming the files and directories in the
   * directory denoted by this abstract pathname.
   *
   * <p> If this abstract pathname does not denote a directory, then this
   * method returns {@code null}.  Otherwise an array of strings is
   * returned, one for each file or directory in the directory.  Names
   * denoting the directory itself and the directory's parent directory are
   * not included in the result.  Each string is a file name rather than a
   * complete path.
   *
   * <p> There is no guarantee that the name strings in the resulting array
   * will appear in any specific order; they are not, in particular,
   * guaranteed to appear in alphabetical order.
   *
   * <p> Note that the {@link java.nio.file.Files} class defines the {@link
   * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method to
   * open a directory and iterate over the names of the files in the directory.
   * This may use less resources when working with very large directories, and
   * may be more responsive when working with remote directories.
   *
   * @return An array of strings naming the files and directories in the directory denoted by this
   * abstract pathname.  The array will be empty if the directory is empty.  Returns {@code null} if
   * this abstract pathname does not denote a directory, or if an I/O error occurs.
   * @throws SecurityException If a security manager exists and its {@link
   * SecurityManager#checkRead(String)} method denies read access to the directory
   */
  public String[] list() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkRead(path);
    }
    if (isInvalid()) {
      return null;
    }
    return fs.list(this);
  }

  /**
   * Returns an array of strings naming the files and directories in the
   * directory denoted by this abstract pathname that satisfy the specified
   * filter.  The behavior of this method is the same as that of the
   * {@link #list()} method, except that the strings in the returned array
   * must satisfy the filter.  If the given {@code filter} is {@code null}
   * then all names are accepted.  Otherwise, a name satisfies the filter if
   * and only if the value {@code true} results when the {@link
   * FilenameFilter#accept FilenameFilter.accept(File,&nbsp;String)} method
   * of the filter is invoked on this abstract pathname and the name of a
   * file or directory in the directory that it denotes.
   *
   * @param filter A filename filter
   * @return An array of strings naming the files and directories in the directory denoted by this
   * abstract pathname that were accepted by the given {@code filter}.  The array will be empty if
   * the directory is empty or if no names were accepted by the filter. Returns {@code null} if this
   * abstract pathname does not denote a directory, or if an I/O error occurs.
   * @throws SecurityException If a security manager exists and its {@link
   * SecurityManager#checkRead(String)} method denies read access to the directory
   * @see java.nio.file.Files#newDirectoryStream(Path, String)
   */
  public String[] list(FilenameFilter filter) {
    String names[] = list();
    if ((names == null) || (filter == null)) {
      return names;
    }
    List<String> v = new ArrayList<>();
    for (int i = 0; i < names.length; i++) {
      if (filter.accept(this, names[i])) {
        v.add(names[i]);
      }
    }
    return v.toArray(new String[v.size()]);
  }

  /**
   * Returns an array of abstract pathnames denoting the files in the
   * directory denoted by this abstract pathname.
   *
   * <p> If this abstract pathname does not denote a directory, then this
   * method returns {@code null}.  Otherwise an array of {@code File} objects
   * is returned, one for each file or directory in the directory.  Pathnames
   * denoting the directory itself and the directory's parent directory are
   * not included in the result.  Each resulting abstract pathname is
   * constructed from this abstract pathname using the {@link #File(File,
   * String) File(File,&nbsp;String)} constructor.  Therefore if this
   * pathname is absolute then each resulting pathname is absolute; if this
   * pathname is relative then each resulting pathname will be relative to
   * the same directory.
   *
   * <p> There is no guarantee that the name strings in the resulting array
   * will appear in any specific order; they are not, in particular,
   * guaranteed to appear in alphabetical order.
   *
   * <p> Note that the {@link java.nio.file.Files} class defines the {@link
   * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method
   * to open a directory and iterate over the names of the files in the
   * directory. This may use less resources when working with very large
   * directories.
   *
   * @return An array of abstract pathnames denoting the files and directories in the directory
   * denoted by this abstract pathname. The array will be empty if the directory is empty.  Returns
   * {@code null} if this abstract pathname does not denote a directory, or if an I/O error occurs.
   * @throws SecurityException If a security manager exists and its {@link
   * SecurityManager#checkRead(String)} method denies read access to the directory
   * @since 1.2
   */
  public File[] listFiles() {
    String[] ss = list();
    if (ss == null) {
      return null;
    }
    int n = ss.length;
    File[] fs = new File[n];
    for (int i = 0; i < n; i++) {
      fs[i] = new File(ss[i], this);
    }
    return fs;
  }

  /**
   * Returns an array of abstract pathnames denoting the files and
   * directories in the directory denoted by this abstract pathname that
   * satisfy the specified filter.  The behavior of this method is the same
   * as that of the {@link #listFiles()} method, except that the pathnames in
   * the returned array must satisfy the filter.  If the given {@code filter}
   * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
   * satisfies the filter if and only if the value {@code true} results when
   * the {@link FilenameFilter#accept
   * FilenameFilter.accept(File,&nbsp;String)} method of the filter is
   * invoked on this abstract pathname and the name of a file or directory in
   * the directory that it denotes.
   *
   * @param filter A filename filter
   * @return An array of abstract pathnames denoting the files and directories in the directory
   * denoted by this abstract pathname. The array will be empty if the directory is empty.  Returns
   * {@code null} if this abstract pathname does not denote a directory, or if an I/O error occurs.
   * @throws SecurityException If a security manager exists and its {@link
   * SecurityManager#checkRead(String)} method denies read access to the directory
   * @see java.nio.file.Files#newDirectoryStream(Path, String)
   * @since 1.2
   */
  public File[] listFiles(FilenameFilter filter) {
    String ss[] = list();
    if (ss == null) {
      return null;
    }
    ArrayList<File> files = new ArrayList<>();
    for (String s : ss) {
      if ((filter == null) || filter.accept(this, s)) {
        files.add(new File(s, this));
      }
    }
    return files.toArray(new File[files.size()]);
  }

  /**
   * Returns an array of abstract pathnames denoting the files and
   * directories in the directory denoted by this abstract pathname that
   * satisfy the specified filter.  The behavior of this method is the same
   * as that of the {@link #listFiles()} method, except that the pathnames in
   * the returned array must satisfy the filter.  If the given {@code filter}
   * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
   * satisfies the filter if and only if the value {@code true} results when
   * the {@link FileFilter#accept FileFilter.accept(File)} method of the
   * filter is invoked on the pathname.
   *
   * @param filter A file filter
   * @return An array of abstract pathnames denoting the files and directories in the directory
   * denoted by this abstract pathname. The array will be empty if the directory is empty.  Returns
   * {@code null} if this abstract pathname does not denote a directory, or if an I/O error occurs.
   * @throws SecurityException If a security manager exists and its {@link
   * SecurityManager#checkRead(String)} method denies read access to the directory
   * @see java.nio.file.Files#newDirectoryStream(Path, java.nio.file.DirectoryStream.Filter)
   * @since 1.2
   */
  public File[] listFiles(FileFilter filter) {
    String ss[] = list();
    if (ss == null) {
      return null;
    }
    ArrayList<File> files = new ArrayList<>();
    for (String s : ss) {
      File f = new File(s, this);
      if ((filter == null) || filter.accept(f)) {
        files.add(f);
      }
    }
    return files.toArray(new File[files.size()]);
  }

  /**
   * Creates the directory named by this abstract pathname.
   *
   * @return <code>true</code> if and only if the directory was created; <code>false</code>
   * otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method does not permit the named
   * directory to be created
   */
  public boolean mkdir() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.createDirectory(this);
  }

  /**
   * Creates the directory named by this abstract pathname, including any
   * necessary but nonexistent parent directories.  Note that if this
   * operation fails it may have succeeded in creating some of the necessary
   * parent directories.
   *
   * @return <code>true</code> if and only if the directory was created, along with all necessary
   * parent directories; <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkRead(java.lang.String)}</code> method does not permit
   * verification of the existence of the named directory and all necessary parent directories; or
   * if the <code>{@link java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method does
   * not permit the named directory and all necessary parent directories to be created
   */
  public boolean mkdirs() {
    if (exists()) {
      return false;
    }
    if (mkdir()) {
      return true;
    }
    File canonFile = null;
    try {
      canonFile = getCanonicalFile();
    } catch (IOException e) {
      return false;
    }

    File parent = canonFile.getParentFile();
    return (parent != null && (parent.mkdirs() || parent.exists()) &&
        canonFile.mkdir());
  }

  /**
   * Renames the file denoted by this abstract pathname.
   *
   * <p> Many aspects of the behavior of this method are inherently
   * platform-dependent: The rename operation might not be able to move a
   * file from one filesystem to another, it might not be atomic, and it
   * might not succeed if a file with the destination abstract pathname
   * already exists.  The return value should always be checked to make sure
   * that the rename operation was successful.
   *
   * <p> Note that the {@link java.nio.file.Files} class defines the {@link
   * java.nio.file.Files#move move} method to move or rename a file in a
   * platform independent manner.
   *
   * @param dest The new abstract pathname for the named file
   * @return <code>true</code> if and only if the renaming succeeded; <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * either the old or new pathnames
   * @throws NullPointerException If parameter <code>dest</code> is <code>null</code>
   */
  public boolean renameTo(File dest) {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
      security.checkWrite(dest.path);
    }
    if (dest == null) {
      throw new NullPointerException();
    }
    if (this.isInvalid() || dest.isInvalid()) {
      return false;
    }
    return fs.rename(this, dest);
  }

  /**
   * Sets the last-modified time of the file or directory named by this
   * abstract pathname.
   *
   * <p> All platforms support file-modification times to the nearest second,
   * but some provide more precision.  The argument will be truncated to fit
   * the supported precision.  If the operation succeeds and no intervening
   * operations on the file take place, then the next invocation of the
   * <code>{@link #lastModified}</code> method will return the (possibly
   * truncated) <code>time</code> argument that was passed to this method.
   *
   * @param time The new last-modified time, measured in milliseconds since the epoch (00:00:00 GMT,
   * January 1, 1970)
   * @return <code>true</code> if and only if the operation succeeded; <code>false</code> otherwise
   * @throws IllegalArgumentException If the argument is negative
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the named file
   * @since 1.2
   */
  public boolean setLastModified(long time) {
    if (time < 0) {
      throw new IllegalArgumentException("Negative time");
    }
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.setLastModifiedTime(this, time);
  }

  /**
   * Marks the file or directory named by this abstract pathname so that
   * only read operations are allowed. After invoking this method the file
   * or directory will not change until it is either deleted or marked
   * to allow write access. On some platforms it may be possible to start the
   * Java virtual machine with special privileges that allow it to modify
   * files that are marked read-only. Whether or not a read-only file or
   * directory may be deleted depends upon the underlying system.
   *
   * @return <code>true</code> if and only if the operation succeeded; <code>false</code> otherwise
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the named file
   * @since 1.2
   */
  public boolean setReadOnly() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.setReadOnly(this);
  }

  /**
   * Sets the owner's or everybody's write permission for this abstract
   * pathname. On some platforms it may be possible to start the Java virtual
   * machine with special privileges that allow it to modify files that
   * disallow write operations.
   *
   * <p> The {@link java.nio.file.Files} class defines methods that operate on
   * file attributes including file permissions. This may be used when finer
   * manipulation of file permissions is required.
   *
   * @param writable If <code>true</code>, sets the access permission to allow write operations; if
   * <code>false</code> to disallow write operations
   * @param ownerOnly If <code>true</code>, the write permission applies only to the owner's write
   * permission; otherwise, it applies to everybody.  If the underlying file system can not
   * distinguish the owner's write permission from that of others, then the permission will apply to
   * everybody, regardless of this value.
   * @return <code>true</code> if and only if the operation succeeded. The operation will fail if
   * the user does not have permission to change the access permissions of this abstract pathname.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the named file
   * @since 1.6
   */
  public boolean setWritable(boolean writable, boolean ownerOnly) {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.setPermission(this, FileSystem.ACCESS_WRITE, writable, ownerOnly);
  }

  /**
   * A convenience method to set the owner's write permission for this abstract
   * pathname. On some platforms it may be possible to start the Java virtual
   * machine with special privileges that allow it to modify files that
   * disallow write operations.
   *
   * <p> An invocation of this method of the form <tt>file.setWritable(arg)</tt>
   * behaves in exactly the same way as the invocation
   *
   * <pre>
   *     file.setWritable(arg, true) </pre>
   *
   * @param writable If <code>true</code>, sets the access permission to allow write operations; if
   * <code>false</code> to disallow write operations
   * @return <code>true</code> if and only if the operation succeeded.  The operation will fail if
   * the user does not have permission to change the access permissions of this abstract pathname.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the file
   * @since 1.6
   */
  public boolean setWritable(boolean writable) {
    return setWritable(writable, true);
  }

  /**
   * Sets the owner's or everybody's read permission for this abstract
   * pathname. On some platforms it may be possible to start the Java virtual
   * machine with special privileges that allow it to read files that are
   * marked as unreadable.
   *
   * <p> The {@link java.nio.file.Files} class defines methods that operate on
   * file attributes including file permissions. This may be used when finer
   * manipulation of file permissions is required.
   *
   * @param readable If <code>true</code>, sets the access permission to allow read operations; if
   * <code>false</code> to disallow read operations
   * @param ownerOnly If <code>true</code>, the read permission applies only to the owner's read
   * permission; otherwise, it applies to everybody.  If the underlying file system can not
   * distinguish the owner's read permission from that of others, then the permission will apply to
   * everybody, regardless of this value.
   * @return <code>true</code> if and only if the operation succeeded.  The operation will fail if
   * the user does not have permission to change the access permissions of this abstract pathname.
   * If <code>readable</code> is <code>false</code> and the underlying file system does not
   * implement a read permission, then the operation will fail.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the file
   * @since 1.6
   */
  public boolean setReadable(boolean readable, boolean ownerOnly) {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.setPermission(this, FileSystem.ACCESS_READ, readable, ownerOnly);
  }

  /**
   * A convenience method to set the owner's read permission for this abstract
   * pathname. On some platforms it may be possible to start the Java virtual
   * machine with special privileges that allow it to read files that that are
   * marked as unreadable.
   *
   * <p>An invocation of this method of the form <tt>file.setReadable(arg)</tt>
   * behaves in exactly the same way as the invocation
   *
   * <pre>
   *     file.setReadable(arg, true) </pre>
   *
   * @param readable If <code>true</code>, sets the access permission to allow read operations; if
   * <code>false</code> to disallow read operations
   * @return <code>true</code> if and only if the operation succeeded.  The operation will fail if
   * the user does not have permission to change the access permissions of this abstract pathname.
   * If <code>readable</code> is <code>false</code> and the underlying file system does not
   * implement a read permission, then the operation will fail.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the file
   * @since 1.6
   */
  public boolean setReadable(boolean readable) {
    return setReadable(readable, true);
  }

  /**
   * Sets the owner's or everybody's execute permission for this abstract
   * pathname. On some platforms it may be possible to start the Java virtual
   * machine with special privileges that allow it to execute files that are
   * not marked executable.
   *
   * <p> The {@link java.nio.file.Files} class defines methods that operate on
   * file attributes including file permissions. This may be used when finer
   * manipulation of file permissions is required.
   *
   * @param executable If <code>true</code>, sets the access permission to allow execute operations;
   * if <code>false</code> to disallow execute operations
   * @param ownerOnly If <code>true</code>, the execute permission applies only to the owner's
   * execute permission; otherwise, it applies to everybody. If the underlying file system can not
   * distinguish the owner's execute permission from that of others, then the permission will apply
   * to everybody, regardless of this value.
   * @return <code>true</code> if and only if the operation succeeded.  The operation will fail if
   * the user does not have permission to change the access permissions of this abstract pathname.
   * If <code>executable</code> is <code>false</code> and the underlying file system does not
   * implement an execute permission, then the operation will fail.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the file
   * @since 1.6
   */
  public boolean setExecutable(boolean executable, boolean ownerOnly) {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkWrite(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.setPermission(this, FileSystem.ACCESS_EXECUTE, executable, ownerOnly);
  }

  /**
   * A convenience method to set the owner's execute permission for this
   * abstract pathname. On some platforms it may be possible to start the Java
   * virtual machine with special privileges that allow it to execute files
   * that are not marked executable.
   *
   * <p>An invocation of this method of the form <tt>file.setExcutable(arg)</tt>
   * behaves in exactly the same way as the invocation
   *
   * <pre>
   *     file.setExecutable(arg, true) </pre>
   *
   * @param executable If <code>true</code>, sets the access permission to allow execute operations;
   * if <code>false</code> to disallow execute operations
   * @return <code>true</code> if and only if the operation succeeded.  The operation will fail if
   * the user does not have permission to change the access permissions of this abstract pathname.
   * If <code>executable</code> is <code>false</code> and the underlying file system does not
   * implement an execute permission, then the operation will fail.
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method denies write access to
   * the file
   * @since 1.6
   */
  public boolean setExecutable(boolean executable) {
    return setExecutable(executable, true);
  }

  /**
   * Tests whether the application can execute the file denoted by this
   * abstract pathname. On some platforms it may be possible to start the
   * Java virtual machine with special privileges that allow it to execute
   * files that are not marked executable. Consequently this method may return
   * {@code true} even though the file does not have execute permissions.
   *
   * @return <code>true</code> if and only if the abstract pathname exists <em>and</em> the
   * application is allowed to execute the file
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkExec(java.lang.String)}</code> method denies execute access to
   * the file
   * @since 1.6
   */
  public boolean canExecute() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkExec(path);
    }
    if (isInvalid()) {
      return false;
    }
    return fs.checkAccess(this, FileSystem.ACCESS_EXECUTE);
  }


    /* -- Filesystem interface -- */

  /**
   * List the available filesystem roots.
   *
   * <p> A particular Java platform may support zero or more
   * hierarchically-organized file systems.  Each file system has a
   * {@code root} directory from which all other files in that file system
   * can be reached.  Windows platforms, for example, have a root directory
   * for each active drive; UNIX platforms have a single root directory,
   * namely {@code "/"}.  The set of available filesystem roots is affected
   * by various system-level operations such as the insertion or ejection of
   * removable media and the disconnecting or unmounting of physical or
   * virtual disk drives.
   *
   * <p> This method returns an array of {@code File} objects that denote the
   * root directories of the available filesystem roots.  It is guaranteed
   * that the canonical pathname of any file physically present on the local
   * machine will begin with one of the roots returned by this method.
   *
   * <p> The canonical pathname of a file that resides on some other machine
   * and is accessed via a remote-filesystem protocol such as SMB or NFS may
   * or may not begin with one of the roots returned by this method.  If the
   * pathname of a remote file is syntactically indistinguishable from the
   * pathname of a local file then it will begin with one of the roots
   * returned by this method.  Thus, for example, {@code File} objects
   * denoting the root directories of the mapped network drives of a Windows
   * platform will be returned by this method, while {@code File} objects
   * containing UNC pathnames will not be returned by this method.
   *
   * <p> Unlike most methods in this class, this method does not throw
   * security exceptions.  If a security manager exists and its {@link
   * SecurityManager#checkRead(String)} method denies read access to a
   * particular root directory, then that directory will not appear in the
   * result.
   *
   * @return An array of {@code File} objects denoting the available filesystem roots, or {@code
   * null} if the set of roots could not be determined.  The array will be empty if there are no
   * filesystem roots.
   * @see java.nio.file.FileStore
   * @since 1.2
   */
  public static File[] listRoots() {
    return fs.listRoots();
  }


    /* -- Disk usage -- */

  /**
   * Returns the size of the partition <a href="#partName">named</a> by this
   * abstract pathname.
   *
   * @return The size, in bytes, of the partition or <tt>0L</tt> if this abstract pathname does not
   * name a partition
   * @throws SecurityException If a security manager has been installed and it denies {@link
   * RuntimePermission}<tt>("getFileSystemAttributes")</tt> or its {@link
   * SecurityManager#checkRead(String)} method denies read access to the file named by this abstract
   * pathname
   * @since 1.6
   */
  public long getTotalSpace() {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
      sm.checkRead(path);
    }
    if (isInvalid()) {
      return 0L;
    }
    return fs.getSpace(this, FileSystem.SPACE_TOTAL);
  }

  /**
   * Returns the number of unallocated bytes in the partition <a
   * href="#partName">named</a> by this abstract path name.
   *
   * <p> The returned number of unallocated bytes is a hint, but not
   * a guarantee, that it is possible to use most or any of these
   * bytes.  The number of unallocated bytes is most likely to be
   * accurate immediately after this call.  It is likely to be made
   * inaccurate by any external I/O operations including those made
   * on the system outside of this virtual machine.  This method
   * makes no guarantee that write operations to this file system
   * will succeed.
   *
   * @return The number of unallocated bytes on the partition or <tt>0L</tt> if the abstract
   * pathname does not name a partition.  This value will be less than or equal to the total file
   * system size returned by {@link #getTotalSpace}.
   * @throws SecurityException If a security manager has been installed and it denies {@link
   * RuntimePermission}<tt>("getFileSystemAttributes")</tt> or its {@link
   * SecurityManager#checkRead(String)} method denies read access to the file named by this abstract
   * pathname
   * @since 1.6
   */
  public long getFreeSpace() {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
      sm.checkRead(path);
    }
    if (isInvalid()) {
      return 0L;
    }
    return fs.getSpace(this, FileSystem.SPACE_FREE);
  }

  /**
   * Returns the number of bytes available to this virtual machine on the
   * partition <a href="#partName">named</a> by this abstract pathname.  When
   * possible, this method checks for write permissions and other operating
   * system restrictions and will therefore usually provide a more accurate
   * estimate of how much new data can actually be written than {@link
   * #getFreeSpace}.
   *
   * <p> The returned number of available bytes is a hint, but not a
   * guarantee, that it is possible to use most or any of these bytes.  The
   * number of unallocated bytes is most likely to be accurate immediately
   * after this call.  It is likely to be made inaccurate by any external
   * I/O operations including those made on the system outside of this
   * virtual machine.  This method makes no guarantee that write operations
   * to this file system will succeed.
   *
   * @return The number of available bytes on the partition or <tt>0L</tt> if the abstract pathname
   * does not name a partition.  On systems where this information is not available, this method
   * will be equivalent to a call to {@link #getFreeSpace}.
   * @throws SecurityException If a security manager has been installed and it denies {@link
   * RuntimePermission}<tt>("getFileSystemAttributes")</tt> or its {@link
   * SecurityManager#checkRead(String)} method denies read access to the file named by this abstract
   * pathname
   * @since 1.6
   */
  public long getUsableSpace() {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
      sm.checkRead(path);
    }
    if (isInvalid()) {
      return 0L;
    }
    return fs.getSpace(this, FileSystem.SPACE_USABLE);
  }

    /* -- Temporary files -- */

  private static class TempDirectory {

    private TempDirectory() {
    }

    // temporary directory location
    private static final File tmpdir = new File(AccessController
        .doPrivileged(new GetPropertyAction("java.io.tmpdir")));

    static File location() {
      return tmpdir;
    }

    // file name generation
    private static final SecureRandom random = new SecureRandom();

    static File generateFile(String prefix, String suffix, File dir)
        throws IOException {
      long n = random.nextLong();
      if (n == Long.MIN_VALUE) {
        n = 0;      // corner case
      } else {
        n = Math.abs(n);
      }

      // Use only the file name from the supplied prefix
      prefix = (new File(prefix)).getName();

      String name = prefix + Long.toString(n) + suffix;
      File f = new File(dir, name);
      if (!name.equals(f.getName()) || f.isInvalid()) {
        if (System.getSecurityManager() != null) {
          throw new IOException("Unable to create temporary file");
        } else {
          throw new IOException("Unable to create temporary file, " + f);
        }
      }
      return f;
    }
  }

  /**
   * <p> Creates a new empty file in the specified directory, using the
   * given prefix and suffix strings to generate its name.  If this method
   * returns successfully then it is guaranteed that:
   *
   * <ol>
   * <li> The file denoted by the returned abstract pathname did not exist
   * before this method was invoked, and
   * <li> Neither this method nor any of its variants will return the same
   * abstract pathname again in the current invocation of the virtual
   * machine.
   * </ol>
   *
   * This method provides only part of a temporary-file facility.  To arrange
   * for a file created by this method to be deleted automatically, use the
   * <code>{@link #deleteOnExit}</code> method.
   *
   * <p> The <code>prefix</code> argument must be at least three characters
   * long.  It is recommended that the prefix be a short, meaningful string
   * such as <code>"hjb"</code> or <code>"mail"</code>.  The
   * <code>suffix</code> argument may be <code>null</code>, in which case the
   * suffix <code>".tmp"</code> will be used.
   *
   * <p> To create the new file, the prefix and the suffix may first be
   * adjusted to fit the limitations of the underlying platform.  If the
   * prefix is too long then it will be truncated, but its first three
   * characters will always be preserved.  If the suffix is too long then it
   * too will be truncated, but if it begins with a period character
   * (<code>'.'</code>) then the period and the first three characters
   * following it will always be preserved.  Once these adjustments have been
   * made the name of the new file will be generated by concatenating the
   * prefix, five or more internally-generated characters, and the suffix.
   *
   * <p> If the <code>directory</code> argument is <code>null</code> then the
   * system-dependent default temporary-file directory will be used.  The
   * default temporary-file directory is specified by the system property
   * <code>java.io.tmpdir</code>.  On UNIX systems the default value of this
   * property is typically <code>"/tmp"</code> or <code>"/var/tmp"</code>; on
   * Microsoft Windows systems it is typically <code>"C:\\WINNT\\TEMP"</code>.  A different
   * value may be given to this system property when the Java virtual machine
   * is invoked, but programmatic changes to this property are not guaranteed
   * to have any effect upon the temporary directory used by this method.
   *
   * @param prefix The prefix string to be used in generating the file's name; must be at least
   * three characters long
   * @param suffix The suffix string to be used in generating the file's name; may be
   * <code>null</code>, in which case the suffix <code>".tmp"</code> will be used
   * @param directory The directory in which the file is to be created, or <code>null</code> if the
   * default temporary-file directory is to be used
   * @return An abstract pathname denoting a newly-created empty file
   * @throws IllegalArgumentException If the <code>prefix</code> argument contains fewer than three
   * characters
   * @throws IOException If a file could not be created
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method does not allow a file to
   * be created
   * @since 1.2
   */
  public static File createTempFile(String prefix, String suffix,
      File directory)
      throws IOException {
    if (prefix.length() < 3) {
      throw new IllegalArgumentException("Prefix string too short");
    }
    if (suffix == null) {
      suffix = ".tmp";
    }

    File tmpdir = (directory != null) ? directory
        : TempDirectory.location();
    SecurityManager sm = System.getSecurityManager();
    File f;
    do {
      f = TempDirectory.generateFile(prefix, suffix, tmpdir);

      if (sm != null) {
        try {
          sm.checkWrite(f.getPath());
        } catch (SecurityException se) {
          // don't reveal temporary directory location
          if (directory == null) {
            throw new SecurityException("Unable to create temporary file");
          }
          throw se;
        }
      }
    } while ((fs.getBooleanAttributes(f) & FileSystem.BA_EXISTS) != 0);

    if (!fs.createFileExclusively(f.getPath())) {
      throw new IOException("Unable to create temporary file");
    }

    return f;
  }

  /**
   * Creates an empty file in the default temporary-file directory, using
   * the given prefix and suffix to generate its name. Invoking this method
   * is equivalent to invoking <code>{@link #createTempFile(java.lang.String,
   * java.lang.String, java.io.File)
   * createTempFile(prefix,&nbsp;suffix,&nbsp;null)}</code>.
   *
   * <p> The {@link
   * java.nio.file.Files#createTempFile(String, String, java.nio.file.attribute.FileAttribute[])
   * Files.createTempFile} method provides an alternative method to create an
   * empty file in the temporary-file directory. Files created by that method
   * may have more restrictive access permissions to files created by this
   * method and so may be more suited to security-sensitive applications.
   *
   * @param prefix The prefix string to be used in generating the file's name; must be at least
   * three characters long
   * @param suffix The suffix string to be used in generating the file's name; may be
   * <code>null</code>, in which case the suffix <code>".tmp"</code> will be used
   * @return An abstract pathname denoting a newly-created empty file
   * @throws IllegalArgumentException If the <code>prefix</code> argument contains fewer than three
   * characters
   * @throws IOException If a file could not be created
   * @throws SecurityException If a security manager exists and its <code>{@link
   * java.lang.SecurityManager#checkWrite(java.lang.String)}</code> method does not allow a file to
   * be created
   * @see java.nio.file.Files#createTempDirectory(String, FileAttribute[])
   * @since 1.2
   */
  public static File createTempFile(String prefix, String suffix)
      throws IOException {
    return createTempFile(prefix, suffix, null);
  }

    /* -- Basic infrastructure -- */

  /**
   * Compares two abstract pathnames lexicographically.  The ordering
   * defined by this method depends upon the underlying system.  On UNIX
   * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
   * systems it is not.
   *
   * @param pathname The abstract pathname to be compared to this abstract pathname
   * @return Zero if the argument is equal to this abstract pathname, a value less than zero if this
   * abstract pathname is lexicographically less than the argument, or a value greater than zero if
   * this abstract pathname is lexicographically greater than the argument
   * @since 1.2
   */
  public int compareTo(File pathname) {
    return fs.compare(this, pathname);
  }

  /**
   * Tests this abstract pathname for equality with the given object.
   * Returns <code>true</code> if and only if the argument is not
   * <code>null</code> and is an abstract pathname that denotes the same file
   * or directory as this abstract pathname.  Whether or not two abstract
   * pathnames are equal depends upon the underlying system.  On UNIX
   * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
   * systems it is not.
   *
   * @param obj The object to be compared with this abstract pathname
   * @return <code>true</code> if and only if the objects are the same; <code>false</code> otherwise
   */
  public boolean equals(Object obj) {
    if ((obj != null) && (obj instanceof File)) {
      return compareTo((File) obj) == 0;
    }
    return false;
  }

  /**
   * Computes a hash code for this abstract pathname.  Because equality of
   * abstract pathnames is inherently system-dependent, so is the computation
   * of their hash codes.  On UNIX systems, the hash code of an abstract
   * pathname is equal to the exclusive <em>or</em> of the hash code
   * of its pathname string and the decimal value
   * <code>1234321</code>.  On Microsoft Windows systems, the hash
   * code is equal to the exclusive <em>or</em> of the hash code of
   * its pathname string converted to lower case and the decimal
   * value <code>1234321</code>.  Locale is not taken into account on
   * lowercasing the pathname string.
   *
   * @return A hash code for this abstract pathname
   */
  public int hashCode() {
    return fs.hashCode(this);
  }

  /**
   * Returns the pathname string of this abstract pathname.  This is just the
   * string returned by the <code>{@link #getPath}</code> method.
   *
   * @return The string form of this abstract pathname
   */
  public String toString() {
    return getPath();
  }

  /**
   * WriteObject is called to save this filename.
   * The separator character is saved also so it can be replaced
   * in case the path is reconstituted on a different host type.
   * <p>
   *
   * @serialData Default fields followed by separator character.
   */
  private synchronized void writeObject(java.io.ObjectOutputStream s)
      throws IOException {
    s.defaultWriteObject();
    s.writeChar(separatorChar); // Add the separator character
  }

  /**
   * readObject is called to restore this filename.
   * The original separator character is read.  If it is different
   * than the separator character on this system, then the old separator
   * is replaced by the local separator.
   */
  private synchronized void readObject(java.io.ObjectInputStream s)
      throws IOException, ClassNotFoundException {
    ObjectInputStream.GetField fields = s.readFields();
    String pathField = (String) fields.get("path", null);
    char sep = s.readChar(); // read the previous separator char
    if (sep != separatorChar) {
      pathField = pathField.replace(sep, separatorChar);
    }
    String path = fs.normalize(pathField);
    UNSAFE.putObject(this, PATH_OFFSET, path);
    UNSAFE.putIntVolatile(this, PREFIX_LENGTH_OFFSET, fs.prefixLength(path));
  }

  private static final long PATH_OFFSET;
  private static final long PREFIX_LENGTH_OFFSET;
  private static final sun.misc.Unsafe UNSAFE;

  static {
    try {
      sun.misc.Unsafe unsafe = sun.misc.Unsafe.getUnsafe();
      PATH_OFFSET = unsafe.objectFieldOffset(
          File.class.getDeclaredField("path"));
      PREFIX_LENGTH_OFFSET = unsafe.objectFieldOffset(
          File.class.getDeclaredField("prefixLength"));
      UNSAFE = unsafe;
    } catch (ReflectiveOperationException e) {
      throw new Error(e);
    }
  }


  /**
   * use serialVersionUID from JDK 1.0.2 for interoperability
   */
  private static final long serialVersionUID = 301077366599181567L;

  // -- Integration with java.nio.file --

  private volatile transient Path filePath;

  /**
   * Returns a {@link Path java.nio.file.Path} object constructed from the
   * this abstract path. The resulting {@code Path} is associated with the
   * {@link java.nio.file.FileSystems#getDefault default-filesystem}.
   *
   * <p> The first invocation of this method works as if invoking it were
   * equivalent to evaluating the expression:
   * <blockquote><pre>
   * {@link java.nio.file.FileSystems#getDefault FileSystems.getDefault}().{@link
   * java.nio.file.FileSystem#getPath getPath}(this.{@link #getPath getPath}());
   * </pre></blockquote>
   * Subsequent invocations of this method return the same {@code Path}.
   *
   * <p> If this abstract pathname is the empty abstract pathname then this
   * method returns a {@code Path} that may be used to access the current
   * user directory.
   *
   * @return a {@code Path} constructed from this abstract path
   * @throws java.nio.file.InvalidPathException if a {@code Path} object cannot be constructed from
   * the abstract path (see {@link java.nio.file.FileSystem#getPath FileSystem.getPath})
   * @see Path#toFile
   * @since 1.7
   */
  public Path toPath() {
    Path result = filePath;
    if (result == null) {
      synchronized (this) {
        result = filePath;
        if (result == null) {
          result = FileSystems.getDefault().getPath(path);
          filePath = result;
        }
      }
    }
    return result;
  }
}
